In general, children need dental xrays more frequently than adults. Their mouths grow and change rapidly. They are more susceptible than adults to tooth decay. But xrays do much more than detect tooth decay. They survey the erupting teeth, diagnose bone diseases, evaluate the results of an injury, and plan for orthodontic treatment.
Pediatric dentist are particularly careful to minimize the exposure of child patients to radiation. The amount of radiation is incredibly low with modern, digital xrays. In fact, the xray itself presents far smaller risk than undetected and untreated dental problems.